1. Field of the Invention
The present invention relates to a method of forming a pattern. More particularly, the present invention relates to a coatable inorganic material and a method of forming a pattern by utilizing the same.
2. Description of Related Art
According to the minimum spot calculation formula, S≈0.52λ/NA, of a laser beam direct write lithography process, it is known that an exposure device with higher resolution capability is needed to obtain a capability of defining a pattern with higher density or smaller size in a unit area, in which S is the size of an exposure spot, λ is the wavelength of an exposure source, and NA is the numerical aperture (NA) of the system. It is known from the formula that, reducing the wavelength and increasing the NA value can improve the resolution of a laser beam direct write lithography device. However, as for the light source of the laser beam direct write lithography device, the resolution provided by the light source is relative to the wavelength of the light source, so the laser beam direct write lithography has its optical diffraction limit. However, as for the laser beam direct write lithography process, in addition to the resolution capability of the exposure source discussed above, another important factor that affects the pattern definition capability of the laser beam direct write lithography process is the property of the photoresist material. The quality of the property of the photoresist material is reflected by the numerical value k1 in the Rayleigh theory (γ=k1λ/NA), so as to test the resolution capability of pattern definition of the entire laser beam direct write lithography process.
In a conventional deep ultraviolet light (DUV) laser beam direct write lithography process, the photoresist generally used is an organic photoresist system. For a laser beam direct write lithography system with a DUV wavelength of 248 nm, 257 nm, or 266 nm, the maximum NA of an adopted objective lens is 0.9, and the minimum spot size thereof is about 150 nm in theory. The above laser beam direct write lithography system employs two different kinds of photo mode organic photoresists generally used at present, which are I-line photoresist and chemical amplified type photoresist (DUV CA photoresist), respectively, and the contrast (γ) of this kind of photoresist and the obtainable minimum pattern size definition capability are mostly considered in selecting the photoresist. Taking the current research data in general, it is known that the maximum contrast of the I-line photoresist is usually 3, the contrast of the DUV chemical amplified type photoresist is 8, and the optimal pattern resolution thereof can reach the minimum pattern structure size of 130 nm to 180 nm. That is to say, the current DUV laser direct write system with the mentioned organic photoresist cannot meet the requirements of nano-scale pattern definition capability (≦100 nm). Additionally, in regard to I-line photoresist, besides having a contrast not high enough, this type of photoresist also has an insufficient transparency to DUV light, such that this photoresist cannot achieve a higher resolution capability. Although the other type of chemical amplified type photoresist has a higher contrast γ (about two times of that of the I-line photo resist), the polymer main chain of this type of photoresist is easily contaminated by environment, resulting in the limitation of the usage of this type of photoresist. Further, the I-line photoresist and the chemical amplified type photoresist are composed of a polymer with chain structure of high molecular weight. Thus, the surface roughness of the pattern after development becomes higher due to the molecular cluster property of the polymer.
As described above, for the current DUV laser of 248/257/266 nm and the laser beam direct write lithography system with a high NA of 0.9, if the laser wavelength is further reduced or a near-field optical laser beam direct write lithography system (NA>1) is developed, the mechanical precision and the control precision must be improved, and the component cost and production cost of the device will be greatly increased, thus limiting the development thereof. Therefore, in the nano-scale laser beam direct write lithography technique, it is a major issue to be solved urgently on how to overcome the optical diffraction limit of the laser beam direct write lithography machine. The possibility of using a material process technique together with the existing laser beam direct write lithography system as a solution can not only overcome the seemingly insuperable optical diffraction limit, but also effectively reduce the production cost of the device. Therefore, the objective of the present invention is to improve the pattern definition capability of the laser beam direct write lithography system to reach the nano-scale by developing a novel resist material with a higher resolution capability and a related fabrication method to overcome the laser optical diffraction limit.
In the application development of the nano-scale laser beam direct write lithography, recently a technique of phase transition laser beam direct write lithography process of film formation by a sputtering process has been applied in the current laser beam direct write system, and the steps thereof are as shown in FIG. 1.
Referring to FIG. 1, firstly, in Step 100, a substrate is provided, and then a phase change metal or oxide target material is sputtered on the substrate in the manner of sputtering film formation by a high-vacuum sputtering system (Step 102), and most of this type of inorganic resist material can complete the laser beam direct write lithography process by controlling the phase change between the crystalline and amorphous phase of the alloy thin film. The sputtering resist generally is a chalcogenide material or a metal oxide formed by sputtering, and in this figure a layer of chalcogenide material is taken as an example. Afterward, the layer of chalcogenide material is exposed by a laser (Step 104). Then, an additional specific wet etchant is needed to reserve or remove the region generated through thermochemical reaction, i.e., to develop, so as to form a pattern (Step 106). The resist of the phase change laser beam direct write lithography is an inorganic thermal-mode resist. The reactivity of this type of resist is non-linear, and the heat thereof can be dissipated by diffusion, so the exposure mechanism is stopped. Therefore, this type of resist has a better resolution capability compared with the conventional organic photo mode photoresist recording, and can overcome the optical diffraction limit effectively, i.e., a small pattern can be defined and fabricated by a laser beam direct write lithography with this type of resist.
However, the sputtering phase transition laser beam direct write lithography technique adopts a phase change metal resist film that is sputtered by a high-cost and complicated vacuum sputtering coating system, such that the device cost is much higher than that of the conventional photoresist spin coating film-formation process and the etchant is special. Additionally, the reflectance of the film layer of phase change metal resist is too high, and cannot be used in a focus servo system of the convention laser beam direct write lithography machine. If the film layer of phase change metal resist, utilized in the sputtering phase change laser beam direct write lithography technique, is adopted, it is needed to purchase an entirely new process device, thus resulting in a great increment in the investment of the device.